The present invention relates to an osteosynthesis device for a trochanteric or trochanteric-diaphyseal fracture.
Reduction of such a fracture and holding the parts of the fractured bone for the time taken for the bone to consolidate requires insertion of at least one screw inside the femoral neck, said screw being supported both in the femoral head and in the cortex of the bone.
For this specific type of fracture, repair of which requires firm diaphyseal support, U.S. Pat. No. 4,827,917 teaches the use of a medullary rod which is locked at its distal part and which at its proximal part has at least one hole provided along an axis essentially parallel to the axis of the femoral neck, the aforesaid screw being designed to pass through this hole and be immobilized relative to the rod.
Preferably, self-drilling, self-tapping screws are used, which screws have a threaded distal end with a diameter larger than that of the shaft. In this case, as shown in European Patent Application No. 0 441 577 or German Utility Model No. 92 06 580, the aforesaid hole is provided in the rod having the diameter of the threaded distal end of the screw and, after the latter has been set in place, a sleeve is fitted onto the proximal end of the screw and through the hole in the rod to fill the space between the shaft of the screw and the rod.
The rod, generally tubular, is tapped at its proximal end, allowing installation of an adjusting screw which immobilizes the screw engaged in the bone or the sleeve engaged on the screw, relative to the rod.
This means of immobilization has the drawback of being complex in use, since it is necessary to screw in and tighten this adjusting screw at the proximal end of the rod while keeping the rod and screw in their proper relative positions.
Moreover, in view of the angle formed by the screw and the rod, the bearing surface of the end of the adjusting screw against the screw engaged in the bone or the aforesaid sleeve is limited, so that the possibility of play between the rod and the screw or the sleeve may occur over time, under the effect of repeated forces applied to this precise spot on the bone. A large tightening torque is necessary to minimize this risk of play, which contributes to making the installation of these devices complex.
Finally, such an adjusting screw makes the manufacture of these devices complex.
Moreover, in the prior devices, the screw or screws is/are immobilized rigidly relative to the rod. This rigid assembly proves to be undesirable for full consolidation of the bone since the positioning of the parts of the fractured bone may evolve in the course of bone consolidation. In certain extreme cases, the distal ends of the screws engaged in the bone may have traversed the femoral head in the course of bone consolidation.
The goal of the invention is to overcome these drawbacks.